In the construction of masonry buildings, it is often necessary to anchor metal framework within the building after the concrete work has been completed. The practice at the present time is to drill blind holes into the concrete walls and insert expansion bolts which when tightened expand sufficiently to somewhat distort the walls of the holes and thereby anchor to them. However, it has been the experience of the prior art that over a period of time this type of anchor assembly loosens, and may be rather easily withdrawn from the hole. The loosening occurs partly as a result of relaxation of the contact pressures built up by a very small increment of expansion, and partly as a result of vibrations in the building over a period of time. This is particularly to be avoided in the case of power plants, and study has been put into making a more secure expansion bolt assembly which will not relax its grip over a period of time.
The present invention provides an anchor bolt of a general type which is well-known in the prior art. Typical examples of such anchor bolts are shown in U.S. Pat. Nos. 1,850,768 to Peirce and 4,137,816 to Gartner.
U.S. Pat. No. 4,011,786 to Liebig shows a structure in which the expansion sleeve is slotted, and has an annular groove around it where the leg portions join the cylindrical portions so as to facilitate expansion of the legs when the cone is drawn into them.
Copies of these three patents are included with this application as originally filed.